config: Parse model from YAML

[pellared]

Implement https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md#parse for YAML.

[pellared]

PTAL @codeboten

[carrbs]

@codeboten , @pellared should I implement this, (and remove the comment about JSON?), since we are likely just implementing for YAML atm?

opentelemetry-go-contrib/config/config.go

Lines 116 to 118 in 96790b3

	// TODO: implement parsing functionality:
	// - https://github.com/open-telemetry/opentelemetry-go-contrib/issues/4373
	// - https://github.com/open-telemetry/opentelemetry-go-contrib/issues/4412

[pellared]

Works for me but I am leaving the decision to @codeboten

[codeboten]

i think thats a sensible way forward

[carrbs]

Spent some more time looking into this and I have questions on what the scope of this issue is. I'm new to otel, so hopefully you can give me some grace if there are obvious oversights or overly simple questions.

I can see that this repo is leveraging the "official" opentelemetry specification schema to render the generated_config.go file.

1. Should the Parse(config_file) function utilize this generated config for validation?
2. Is the purpose to ensure that all known properties from the generated config map from the input YAML to the expected structs in the generated config file, or just to focus on the environment variable handling?
3. If the YAML input file contains mapping unknown to the schema, how is that handled?
   • The examples describing the nuance around environment variables are not part of the schema, and I also saw the "additionalProperties": true on the schema ☝️.

Any thoughts on this would be awesome, I'd be happy to help on this but if it's not high priority we can table it :)

[MadVikingGod]

The current generated config uses the mapstructure tags. This means that parsing yaml (and json) is done by marshaling raw yaml into a map[string]interface{} and then using the mapstructure package to Decode() the map into the actual config.

I think it might be best if we have an example of this.

[pellared]

Regarding env var substitution: open-telemetry/opentelemetry-specification#3914 (comment)

[codeboten]

Thanks all for the patience, I'm finally getting back to the work on the config package.

2. Is the purpose to ensure that all known properties from the generated config map from the input YAML to the expected structs in the generated config file, or just to focus on the environment variable handling?

Ideally yes. It's okay to implement these as we go, as in I wouldn't worry about supporting everything right away, we can always add new issues for features that are not supported, this is how the development has been done so far :)

3. If the YAML input file contains mapping unknown to the schema, how is that handled?

   • The examples describing the nuance around environment variables are not part of the schema, and I also saw the "additionalProperties": true on the schema ☝️.

@carrbs Support for additional properties should be addressed by #4832. I submitted a prototype upstream to the go-jsonschema library and it's since been implemented in the library.

The current generated config uses the mapstructure tags. This means that parsing yaml (and json) is done by marshaling raw yaml into a map[string]interface{} and then using the mapstructure package to Decode() the map into the actual config.

@MadVikingGod Correct, this is what the Collector does today with this configuration. I don't know if we have a strong preference taking this in a different direction, if we wanted to support additional struct tags. I'm open to ideas from the maintainers/approvers in this community.

[codeboten]

@MadVikingGod @carrbs an alternative is to generate the yaml struct tags and avoid the mapstructure middle step, see #5433 as an example